The invention relates to a method of micro-working a surface of a workpiece while using a pulsated laser beam which is directed normal to the surface, and it relates in particular to a method of micro-milling such a surface.
Various methods of surface-working by means of a laser are known in practice. For example, when welding by means of a laser beam the material is made to melt, but deformation of the components to be joined and removal of material do not take place. When drilling and cutting by means of a laser beam, material is removed indeed and is carried away through the cut thus formed. It must be ensured that this way of removing material begins as rapidly as possible, for which purpose a rapid evaporation and discharge of the material are required. For this purpose a high power density, which is not necessarily readjusted afterwards, is required upon initiating the cutting process on the workpiece.
In most forms of laser marking, coding or texturing and in laser radiation for adjusting electronic components, a thin layer of material is removed from very local areas. This very thin layer has a high absorbing power for the laser radiation and backed by underlying carrier layer is of a different material which has a very low absorbing power or which reflects the laser radiation. The radiation time is adjusted so that the underlying different material cannot be attacked by transferred thermal energy. Upon hardening metal surfaces the material is heated at the surface and a transformation hardening is produced. During this hardening at the hardening temperature the material should not melt. In other surface finishing methods, for example, surface alloying of metals (alloying and cladding), the material itself or a deposited layer of material is made to melt and, for example, powders are introduced into the melting pool.
Other methods for the precision working of materials are also known, for example, spark erosion, ultrasonic working and etching. In the case of spark erosion an electrode must be used and only conductive material at the surface can be worked. In this connection the problem occurs that the electrode has to be replaced repeatedly. In ultrasonic methods only a rough finishing is possible and in a micro-working method an electrode on a micro scale is required. In etching only a restricted depth can be reached and the problem of over- and under-etching occurs.